Drastic chlorine drop?

[jtb777]

Hi all,

My chlorine level seems to have drastically dropped within the last couple of days. I’d love some advice as to what might have happened.

For the last 2 years, I’ve been using liquid chlorine and have been keeping my CYA level around 40/45. Generally, I’m at a FC 5 or 6 every day.

Two days ago, I was at a 6. Today, it’s barely a 1. We’re having colder weather (low 60’s), no heavy bather load, no unusual organic debris in the pool (that I can see), so I’m at a loss.

I’m using the recommended Taylor testing kit and liquid chlorine (no tablets) to maintain. I did add liquid stabilizer two days ago to boost my CYA from 30 to 45.

The water looks great, but I’ll be dumping a bunch of chlorine tonight when the sun goes down.

I’m pasting my pool data below. Thanks for the help!

———-

Build Type: Plaster
Volume: 30000 gallons
Chemistry: Liquid Chlorine
------------------------------------------
Latest Test Result Summary:
FC: 1.0 (27 minutes ago)
CC: 0.0 (27 minutes ago)
pH: 7.8 (27 minutes ago)
TA: 70 (3 days ago)
CH: 530 (3 days ago)
CYA: 45 (27 minutes ago)
BORATES: 50 (7 months ago)
==========================================
------------------------------------------
Test Results 11-04-2024 @ 11:34 AM
------------------------------------------
Free Chlorine: 1.0
Combined Chlorine: 0.0
pH: 7.8
CYA: 45

------------------------------------------
Maintenance 11-02-2024 @ 03:04 PM
------------------------------------------
Brushed

------------------------------------------
Chemical Addition 11-02-2024 @ 03:04 PM
------------------------------------------
+ 1 Gallons of LiquidStabilizer

------------------------------------------
Chemical Addition 11-01-2024 @ 06:25 PM
------------------------------------------
+ 30.677905005867157 FluidOunces of Bleach

------------------------------------------
Test Results 11-01-2024 @ 10:34 AM
------------------------------------------
Free Chlorine: 5.0
Combined Chlorine: 0.0
pH: 7.8
Total Alkalinity: 70
Calcium Hardness: 530
CYA: 30

------------------------------------------
Chemical Addition 10-29-2024 @ 06:23 PM
------------------------------------------
+ 49.08464800938744 FluidOunces of Bleach

------------------------------------------
Test Results 10-29-2024 @ 11:46 AM
------------------------------------------
Free Chlorine: 5.4
Combined Chlorine: 0.0
pH: 7.8

 

[Mdragger88]

From your logs it looks like you added 1ppm worth of chlorine in the evening on Friday 11/1,
9 daytime hours after testing 5ppm.
now - almost 3 days later your fc is 1ppm.
So a potential 5ppm loss over 3 days (1.66ppm/day)
This doesn’t sound that unusual if you’re having sunny days. Its also possible that your dose didn’t yield what you expected due to degradation- we don’t know because you didn’t test afterwards. Or that after basically a day that you were no longer at 5ppm when you dosed.

Get fc up to target range for your cya of 50 (6-8ppm) and do an
Overnight Chlorine Loss Test

 

[jtb777]

From your logs it looks like you added 1ppm worth of chlorine in the evening on Friday 11/1,
9 daytime hours after testing 5ppm.
now - almost 3 days later your fc is 1ppm.
So a potential 5ppm loss over 3 days (1.66ppm/day)
This doesn’t sound that unusual if you’re having sunny days. Its also possible that your dose didn’t yield what you expected due to degradation- we don’t know because you didn’t test afterwards. Or that after basically a day that you were no longer at 5ppm when you dosed.

Get fc up to target range for your cya of 50 (6-8ppm) and do an
Overnight Chlorine Loss Test

I'll do the test. Thanks!